The coming of the new sometimes causes a complete ditching of the old, and much of value was lost 158 years ago when the British Meteorological Office replaced old mariners’ forecasting systems that employed orbits of moon, sun and planets.
Back then, in the hands of those known in the media as “lunarists”, weather could be determined more than a month ahead.
Because of the deployment of on-the-spot barometric and satellite readouts, weather services today only provide ‘nowcasts’ ranging over the next 1-2 days.
This is because by their own admission after 2 days the estimation of the centre of a cyclonic system can be 1000kms out, and this error doubles for each subsequent day.
Weather is opinion-based, where a committee of mets interpret daily photographs of the tops of clouds, using models subject to different degrees of error.
It is reasonable to allow for a 24hr error because many factors can delay rain, such as rain-cloud levels not yet matching the altitudes of cold air required to form rain, too much ground heat stopping rain from falling or going along with the wrong model. W
e have all heard the phrase “the rain held off”.
Systems can vary in speed. A faster transiting moon (relative to earth) brings faster weather change before the following day, especially around new moons, perigees and lunar equinoxes.
It’s when forecasters are the least accurate.
Terrain, elevation, and proximity to coastlines can affect also changeability.
If weather is a science it is fraught with error.
Weather is generated 10-12 miles up - down to 200 feet, so the potential for a rain system overshooting is up to 80 kms, meaning rain forecast for Auckland could end up in Huntly.
For coastal locations it can mean the rain dump or ‘bomb’ landing out to sea.
If, say our focus is Mangawhai, the error and applicability of 50 miles would encompass the Bay of Islands to Auckland.
Most weather readings, averages etc are gathered by instrumentation at airports, usually windier locations to suit requirements of planes, not farmers.
Windy means a drier location than anywhere else in the surrounding countryside, which becomes a forecasting nightmare for varying terrains with their own microclimates.
For longrange that utilises past data, historic weather gauge readings are unreliable for small amounts of moisture, because drizzle and odd showers are indistinguishable from fog, dew, mist, haze, and frost, therefore can conceal the difference on paper between a fine day and a wet one.
Rain amount is a function of prior evaporation.
The sun only provides heat and cannot cause rain, especially at night. The evaporation cycle can be 3-11 days.
Timing of rain depends on pressure zones, direction of air flows, moon's tidal pull on the air, direction of surface sea currents and height of the sea, all of which are functions of other variables.
In NZ we work with island contingencies, shifts of weather at the shore-line from the surround of ocean, short pattern durations over land and anomalies caused by mountainous land masses that juxtapose the plains.
Weather systems in NZ can be quick to come and to go, with westerlies and southwesterlies predominating.
Although all places are subject to error due to orography, cycles due to repeating lunar positions still rule.
Let’s look at 13 March 2008 - officially the hottest maximum temperature ever recorded in Adelaide. The monthly northern declination of the moon (moon furthest north) arrived that day.
In the month before, the hottest day that month (19 Feb) was within two days of northern declination.
A month later in April, the hottest day (9th) was within one day of northern declination.
Australia's highest ever maximum temperature, the all-time record, was 16 January 1889, at Cloncurry.
It was also northern declination on that day.
In the southern hemisphere northern declinations herald warmer trends, but because northern declination is not the sole factor, 1-2 days must be allowed.
Disregarding exceptions, most summer northern declination days tend to deliver hottest conditions.
This summer our northern declinations are 27-28 December, 24-26 January and 21-23 February.
Perigees also bring extra heat, perhaps for Auckland 8-10 January.
When the moon changes hemispheres in its 27.3 day declination cycle, barometric pressures also change. Kingtides and perigees bring extreme weather patterns.
Distance of new and full moon days from perigee and apogee days determines wetness or dryness of the month ahead.
Waxing moon phases tend to be stronger generators of global earthquakes than waning phases.
The hammer manufacturer cannot be blamed for a bruised thumb. An inaccurate forecast does not invalidate any method.
Forecasters do what they can but interpretation must be the responsibility of the end user. We all have different expectancies and different interpretations of how a forecast affects us.
A hot dry day may be a blessing for hanging washing on a line but a continuing disaster for a drought-prone farm.
Wind and hot updrafts are required for gliding, heavy swells from dying cyclones for surfing, hot calm days for ballooning, and persistent light rain is considered the farmer’s friend.
In NZ there simply isn’t enough news.
It means small things, like who said what, when and where to whom, gets headlines.
Those with nothing much to talk about and little else to do may find satisfaction grumbling incessantly about weather.
If the forecaster gets it wrong they will complain and if he gets it right they will complain about when he didn’t.
Dry hot weather blows from a north desert continent called Australia, and the South Island neighbours the South Pole. Our northerlies can thus be too hot and our southerlies too cold.
The weather is not fickle – it knows exactly what it is doing.
Nether are forecasters fickle, for they know the limitations of their craft. The fickle are those demanding more than a flawed system can deliver.
Forecasters cannot make silk purses from sow’s ears.Ken Ring of www.predictweather.com is author of the Weather Almanac for NZ for 2013 (publisher Random House)
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